One aspect of semiconductor processing involves making contact to or electrical connection with integrated circuitry devices, such as conductors or conductive lines which underlie one or more layers of material provided over a substrate. One prior art method of making such connection utilizes contact pads. These are enlarged conductive areas which are typically rectangular or square in shape and operably connected with the integrated circuitry device with which electrical connection is desired. The enlarged pad area provides a degree of tolerance for mask misalignment to still achieve the desired contact without causing an electrical short with other adjacent circuitry. The larger contact pad areas, however, consume valuable wafer surface area which could desirably be used for additional circuitry.
The problem is exemplified in FIG. 1, where a portion of an integrated circuit is indicated generally at 10. Integrated circuit 10 Comprises a substrate 11 atop which a conductor 12 is formed. An insulative layer 13 is provided over conductor 12 and corresponding substrate surface area adjacent the conductor. A contact opening 14 of a minimum desired dimension is formed through a photoresist layer 19, but because it is slightly misaligned to the left, a corresponding portion of insulative layer 13 directly overlying substrate 11 is undesirably removed. Such can also result in etching into substrate 11, as shown.
One prior art proposed solution is set forth in FIGS. 2 and 3. There, a portion of integrated circuitry 10a includes an insulative or semiconductive substrate 11 having an enlarged contact pad 15 formed thereon. A conductive line 16 is formed over substrate 11 and a connects with contact pad 15. The goal is ultimately to make electrical connection with line 16.
An insulative layer 17 is formed over contact pad 15. A contact opening 18 is targeted to be etched to contact pad 15. As shown, contact pad 15 is made considerably larger than the resultant contact opening 18 to provide a tolerance for contact mask misalignment. As an example, two representative contact mask misalignments are shown (FIG. 2). A first contact mask misalignment is shown in dashed lines at 20 and represents a lateral and rotational displacement of the contact opening from the desired central location shown in solid lines. A second contact mask misalignment is shown in dash-dot lines at 22 and represents a simple misplacement in the negative x-direction. Either way, the contact opening falls within the boundary of the contact pad and the desired electrical connection is made. Accordingly, the wider-dimensioned contact pad tolerates mask misalignments, but at the expense of consuming precious wafer real estate.
This invention grew out of concerns associated with conserving wafer space or area. This invention also grew out of concerns associated with reducing or decreasing the area required, for a contact pad.